Hazardous or toxic waste destruction or containment – Destruction or containment of radioactive waste – By fixation in stable solid media
Reexamination Certificate
1999-10-25
2001-09-18
Mai, Ngoclan (Department: 1742)
Hazardous or toxic waste destruction or containment
Destruction or containment of radioactive waste
By fixation in stable solid media
C588S014000, C588S016000, C588S020000, C210S682000, C405S128350
Reexamination Certificate
active
06291736
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to the field of chemical fixation of hazardous waste materials, including metal-bearing materials and radionuclides and radioactive substances, in debris, soils, solid materials, sludges and materials precipitated or filtered from liquids, rendering such hazardous waste materials within a stabilized, insoluble, non-leachable, non-zeolitic and pH stable form suitable for safe and ecologically-acceptable disposal; typically regulated by the U.S. Department of Energy, the U.S. Environmental Protection Agency (“USEPA”), and others. The ecologically safe state of the treated materials is not altered by exposure of the treated materials to acidic leachate, acid rain, or radioactive groundwater. In addition, the safe state of the treated materials is not altered by exposure to changing weather conditions; including rain, heat, freeze and thaw.
BACKGROUND OF THE INVENTION
Various forms of hazardous wastes pose a serious threat to the environment and safe and cost efficient methods for treating and disposing of these wastes has become increasingly important.
Hazardous wastes containing excessive amounts of leachable lead are banned from land disposal. The regulatory threshold limit under Resource Conservation and Recovery Act is 5 mg/l of leachable lead as measured by TCLP (toxicity characteristic leaching procedure) test criteria, United States Environmental Protection Agency (USEPA) method 1311 (SW-846). Waste materials containing TCLP lead levels in excess of 5 mg/l are defined as lead-toxic hazardous waste and are as such restricted from land-filling under current land ban regulations. The cost of disposing lead toxic hazardous waste materials is in excess of $200.00 per ton plus the cost of transporting the hazardous material to landfills for hazardous wastes, which do not exist in every state. This makes the disposal of lead toxic hazardous waste material very expensive. Therefore, treating the lead-bearing process materials and waste streams to render them non-hazardous by RCRA definition would cut down the costs of transportation and disposal tremendously.
Conventional treatment methods for radionuclides and other radioactive substances can be categorized into three groups: 1) separation; 2) structural containment; and 3) physical stabilization/solidification. These treatment methods are complex, costly, expand volumes, and are only temporary solutions.
Various conventional methods have been tried to remove leachable, mobile radionuclides and radioactive substances from soils and other materials. Removal of contamination from soils and solid materials by leaching, centrifugation, extraction and/or washing procedures is extremely expensive and cost-prohibitive because these methods generate vast quantities of contaminated liquid wastes which require further treatment and disposal.
Conventional solidification methods based on cementation technology require up to twenty-eight (28) days curing time, increase the waste volume and may raise the pH above 12.5. USEPA defines a pH above 12.5 as hazardous. Hardened cementitious material is not conducive to retreatment in the event treatment fails obligatory confirmation testing. Solidification methods utilizing lime kiln dust, calcium carbonate and/or powdered lime for fixation are, at best, temporary solutions. Furthermore, these methods increase the waste volume and mass. A primary concern is that cementitious methods dilute the parameters of concern in the final waste matrix.
In the past, radionuclide and radioactive wastes have been temporarily stored; frequently as a liquid, a sludge, or a contaminated fine-grained solid in conjunction with contaminated soils. The art has recognized that a means must be provided for permanent disposal of these wastes, preferably as non-leachable solids, containing non-migratory radionuclides. Such solids must have certain characteristics which make the solids safe and economical for the long term (10
3
to 10
6
years) retention of radioactive isotopes.
SUMMARY OF THE INVENTION
The present invention discloses a method of treating hazardous waste materials, including metal-bearing materials and radionuclides and radioactive substances.
One embodiment of the present invention relates to a chemical treatment technology for immobilizing leachable lead in contaminated soils and solid waste materials. According to the present invention, a process for treating lead-toxic solid wastes in order to stabilize the leachable lead is disclosed, comprising the steps of: (i) mixing the solid waste with a sulfate compound, such as calcium sulfate dihydrate (gypsum powder) or sulfuric acid, having at least one sulfate ion for contacting waste particles and reacting with said leachable lead to produce a substantially insoluble lead composition, such as anglesite and/or calcium-substituted anglesite; and, (ii) mixing said solid waste and sulfate compound with a phosphate reagent, such as phosphoric acid, having at least one phosphate ion for reacting with said leachable lead to produce a substantially insoluble lead composition. The treated material from this process is substantially solid in form and passes the Paint Filter Test while satisfying the regulatory standard for TCLP lead. In all instances, application of this process has been found very reliable in meeting the treatment objectives and in consistently decreasing waste volume.
It is an object of the present invention to provide a technology for treatment of lead-containing solid waste and soil that produces an acceptably low level of leachable lead in the final product to comply with the statutory requirements of TCLP and to pass the Paint Filter Test.
Another object of the invention is to provide such a process while producing no wastewater or secondary waste streams during said process.
Still another object of the invention is to provide such a process which also causes the solid waste material to undergo a volume reduction as a result of treatment.
Yet another object of the invention is to cause fixation of the leachable lead in the solid waste that is permanent under both ordinary and extreme environmental conditions.
The present invention relates to treatment methods employed to chemically convert leachable metal in metal-bearing solid and liquid waste materials to a non-leachable form by mixing the material with one or a combination of components, for example, lime or gypsum and phosphoric acid. The solid and liquid waste materials include contaminated sludges, slurries, soils, waste waters, spent carbon, sand, wire chips, plastic fluff, cracked battery casings, bird and buck shots and tetraethyl lead contaminated organic peat and muck. The metal-bearing materials referred to herein which the present invention treats include those materials having leachable lead, aluminum, arsenic (III), barium, bismuth, cadmium, chromium (III), cooper, iron, nickel, selenium, silver and zinc. The present invention discloses a process comprising a single step mixing of one or more treatment additives, and a process comprising a two step mixing wherein the sequence of performing the steps may be reversible. The present invention provides a novel way of treating a plurality of metal-contaminated materials at a wide range of pH. The method works under acidic, alkaline and neutral conditions.
The processes of the present invention provide reactions that convert leachable metals, especially lead, into a non-leachable form which is geochemically stable for indefinite periods and is expected to withstand acid rain impacts as well as the conditions of a landfill environment.
A first group of treatment chemicals for use in the processes of the present invention includes lime, gypsum, alum, halites, Portland cement, and other similar products that can supply sulfates, halites, hydroxides and/or silicates.
A second group consists of treatment chemicals which can supply phosphate ions. This group includes products such as phosphoric acid, pyrophosphates, triple super phosphate (TSP), trisodium phosphate, potassium phosphates,
Chisick Steven A.
Pal Dhiraj
Yost Karl W.
Mai Ngoclan
McDermott Kevin E.
Sevenson Environmental Services, Inc.
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